Water Year 2017: What a Difference a Year Makes

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SEPTEMBER 2017

California Department of Water Resources California Natural Resources Agency State of California What a Difference a Year Makes Water year 2017 (October 1, 2016 to September 30, 2017) dramatically illustrated the variability in California’s annual precipitation, ending the state’s 5-year drought and coming in at second place for statewide runoff, behind the wettest year of 1983. Virtually all of the state Gates on the Sacramento Weir were opened in 2017 to allow water to flow experienced at least average precipitation, from the Sacramento River into the Yolo Bypass. The 1,920-foot long weir, constructed in 1916, is one of multiple structures making up the Sacramento River Flood Control Project. Its manually operated gates are opened based on and key Sierra Nevada watersheds were much forecasted river flows to reduce Sacramento River flood stages downstream of the American River confluence, to reduce flood risk to the metropolitan above average. Governor Brown lifted the Sacramento area. Prior to water year 2017, the gates were last opened in December 2005. proclamation of statewide drought emergency he issued in 2014, although the state-declared emergency remained in selected central California counties experiencing lingering drought impacts. Prior to 2017, California had experienced a decade of largely dry conditions. Eight of the ten preceding water years were dry, and the water years of 2012- 15 set a record for the driest consecutive four- year period of statewide precipitation.

(Above) This radar located at the Bodega Marine Laboratory is part of an atmospheric river observatory funded by the National Oceanic and Atmospheric Administration (NOAA) and DWR. Over the past decade California (DWR and the California Energy Commission) has invested more than $40 million on observing systems and related work to monitor and develop an understanding of the atmospheric river storms that cause major floods and are important contributors to water supply.

2 California Water Year 2017 Precipitation Percent of Average Precipitation (%), 10/1/2016 - 9/17/17 DWR’s eight-station precipitation index for 2017 (which tracks conditions in the largest Central Valley watersheds important for water supplies) set a new record of nearly 95 inches, as compared to the long-term average of 50 inches. Despite near-record wet conditions for statewide total precipitation, 2017 did not approach the 1983 record for April 1 statewide snow water equivalent. Water year 2017 snowpack was still impressive, however, coming in at 163 percent of average on April 1. Water year 2017 did tie 1983 for a different benchmark record, the latest opening (June 29) of Tioga Pass Road at Yosemite National Park, thanks to a storm season that continued active into late spring. As recently as 2015, California had set a record PERCENT OF AVERAGE for minimum April 1 statewide snowpack at only 5 percent of average, for a period that 5 25 50 70 90 100 110 130 150 200 300 Generated 9/16/2016 at Western Regional Climate Center (WRCC) using provisional data. dates back to 1950. NOAA Climate Centers

California Statewide Annual Precipitation (based on July 1 – June 30 year) nces nces

In the decade prior to water year 2017, only water year 2011 was significantly wetter than average. The statewide drought of 2007-09 was followed by the statewide drought of 2012-16. NOAA National Centers for Environmental information, Climate at a Glance: U.S. Time Series, Precipitation, published September 2017, retrieved on September 7, 2017 from http://www.ncdc.noaa.gov/cag/

California Department of Water Resources 3 California Statewide Mean Temperature Departure, October through September Temperatures Degrees (F) Water year 2017 continued a notable trend of warmer statewide temperatures that began in the 1980s. The summer of 2017 2.0 was the warmest on record for much of California with many site-specific temperature records being not just broken but shattered. Downtown San Francisco’s new 0.0 all-time record of 106 degrees was especially notable. Warming temperatures have many consequences, including influencing the percentage of precipitation that falls as -2.0 rain as compared to snow, and affecting runoff through increased evaporation and 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010 through evapotranspiration from vegetation. Black line denotes 11-year running mean Departures from 1949-2005 base period: In the last few years California has experi- Linear trend 1895-present +1.76 ± 0.48°F/100 yr enced record warm average temperatures, Linear trend 1949-present +3.00 ± 1.16°F/100 yr with 2015 holding the record for warmest Linear trend 1975-present +4.25 ± 2.60°F/100 yr water year. Record warm temperatures, Warmest year 59.4°F in 2015 Coldest year 53.4°F in 1917 especially during drought years, complicate Western Regional Climate Center operating the major Central Valley reservoirs to maintain river temperatures needed for Statewide Average Temperature Ranks salmonid species that require cold water at January - August 2017; Period: 1895-2017 certain life stages.

83 Atmospheric Rivers and Flooding 106 106 102 Water year 2017 was noteworthy for the 109 111 109 109 106 111 113 109 large number of atmospheric rivers making 112 115 114 115 116 111 117 114 landfall in California, with the West Coast 120 115 119 119 120 120 116 as a whole experiencing 53 of these 119 115 122 119 121 122 121 123 121 events. Atmospheric rivers, concentrated 116 122 121 121 119 123 bands of water vapor transported by 122 122 123 strong winds, can cause extreme amounts 119 121 of precipitation under the right weather 123 conditions. California receives half of its average annual precipitation from Record Much Below Near Above Much Record December through February. Atmospheric Lowest Below Average Average Average Above Warmest (1) Average Average (123) river storms in January and February Data courtesy of NOAA/ National Centers for Environmental Information (NCEI) created high water conditions throughout

4 California Water Year 2017 much of the state. The February storms Average Temperature Departure from Average (degF), 10/1/2016 - 9/17/17 were especially memorable for the broad geographic extent of the localized flooding they caused in both Northern and Southern California. DWR’s investment, in partnership with NOAA, in a monitoring system tailored to observing atmospheric river storms and improving related flood forecasting ability has yielded big dividends in understanding the role these storms play in California’s climate.

Atmospheric river storms have historically been the source of major California floods, as well as significant contributors to annual water supply. Although California’s wettest years of 1983 and 2017 were fueled by DEGREES FAHRENHEIT atmospheric river storms, they were not -5 -4 -3 -2 -1 0 1 2 3 4 5 years of major floods on the state’s largest Generated 9/16/2016 at WRCC using provisional data. NOAA Climate Centers

Distribution of Landfalling Atmospheric Rivers on the U.S. West Coast (From October 1, 2016, to April 12, 2017)

Atmospheric Atmospheric Water year 2017 River River Count* AR landfall Strength Weak 12 Moderate 21 Strong 13 Extreme 3 ■ Weak: IVT=250–500 kg m-1 s-1 ■ Moderate: IVT=500–750 kg m-1 s-1 ■ Strong: IVT=750–1000 kg m-1 s-1 ■ Extreme: IVT>1000 kg m-1 s-1 IVT = integrated water vapor transport

Figure from Scripps Institution of Oceanography Loca%on of landfall represents posi%on where AR was strongest at landfall. Many ARs move down the coast over %me. This map does not show these areas.

California Department of Water Resources 5 rivers thanks to the timing of individual storms. The most recent water year of major flooding was 1997 (known for the December 1996 – January 1997 New Year’s Day floods).

Prospects for 2018 are Unknown California’s average annual precipitation depends on a small number of atmospheric river storms and is largely based on the number, timing, size, and characteristics of these storms. The absence of several larger storms can tip the balance between a dry year and a wet year. The sensitivity

February 2017 flooding in San Diego’s low-lying Mission Valley, adjacent to the San Diego of the state’s water budget to fluctuations River. Photos courtesy of National Weather Service San Diego. in a small number of storms explains much of the annual variability in California’s California Snow Water Content - Percent of April 1 Average, July 20, 2017 precipitation, which is the highest of North 2017 1982-1983 (max) that in the coterminous United States and contrasts notably with the relatively 2015-2016 small fluctuation in annual precipitation Average experienced in the eastern United States.

2014-2015 1976-1977 (minimum) Developing the ability to predict conditions favorable for atmospheric river storms is key to improving the ability to predict Central 2017 1982-1983 (max) precipitation with longer lead times than

today’s short-term, operational weather 2015-2016 Average forecasts. DWR is working with researchers 2014-2015 at the National Aeronautics and Space (minimum) 1976-1977 Administration and the Scripps Institution of Oceanography to develop first-ever

experimental forecasts of land-falling South 2017 1982-1983 (max) atmospheric rivers, as a step toward encouraging longer-term forecasting Average capability for California. 2015-2016

2014-2015 1976-1977 (minimum) December January February March April May June July

6 California Water Year 2017 Long-Term Forecasts Comparative Variability of Western Precipitation The National Weather Service (NWS) develops operational weather forecasts out to two weeks, although the forecasts are most accurate for individual storms in the first week. The NWS’ Climate Prediction Center (CPC) prepares operational outlooks that cover the sub-seasonal to seasonal (S2S) time period. These longer-term forecasts that span from two weeks to a year in the future would be extremely useful for making many water management decisions, but the skill of present forecasts is not yet adequate to support decision-making. Coefficient of Variation, Water Year 1951-2008 Figure provided courtesy of Mike Dettinger, USGS 0.1 0.2 0.3 0.4 0.5 0.6 0.7 Improving forecasts at S2S timescales is critically needed for improving efficiency of water operations. Much hope has been pinned on using the status of the El Niño – Southern Oscillation (ENSO) as an indicator of seasonal conditions, but the historical record for California shows that precipitation in most of the state has little relationship to ENSO conditions, except for a tendency in Southern California to link La Niña conditions with dryness. The inability to correctly predict April 1st has traditionally been taken as the date of maximum snowpack accumulation in the seasonal precipitation in water year 2016 Sierra Nevada. Snowpack was noticeably absent at the April 1, 2014, snow survey at Phillips during one of the strongest El Niño events of Station adjacent to Highway 50 just west of the Lake Tahoe Basin. Two prior dry years plus a record dry start to the winter of 2013-14 had prompted Governor Brown to issue a statewide record illustrates how much work remains to drought emergency proclamation in January 2014. In contrast, two vehicles are buried in the be done in this area. snow along Donner Pass Road in Soda Springs in April 2017.

California Department of Water Resources 7 Forecasts for 2018 Present forecasting capability cannot provide a reliable prediction for water year 2018. The high annual variability in California’s precipitation means that every year could hold the prospect for record wet conditions such as those experienced in 2017, or for a return to dry conditions. It is possible, for example, that 2017 could have been a wet outlier in long-term sequence of otherwise dry years, similar to the persistent dry conditions that have been experienced in the Colorado River Basin for all of the present century. In the absence of reliable predictive ability, Californians must be prepared for the worst in terms of hydrologic conditions even

Oroville Dam’s spillways were damaged during the early February 2017 storm, ranked as an as we hope for the best. extreme landfalling atmospheric river. In addition to the damage at Oroville, multiple storms in a month that was wet statewide resulted in localized urban flooding in places as diverse as Maxwell, San Jose, and San Diego.

2011 2012 2013 2014

Feather River at Oroville Feather River at Oroville Feather River at Oroville Feather River at Oroville Feather River at Oroville Feather River at Oroville Feather River at Oroville Yuba River near Smartsville Yuba River near Smartsville Yuba River near Smartsville Yuba River near Smartsville Yuba River near Smartsville Yuba River near Smartsville Yuba River near Smartsville Tule River below Lake Success Tule River below Lake Success Tule River below Lake Success Tule River below Lake Success Tule River below Lake Success Tule River below Lake Success Tule River below Lake Success Merced River below Falls Merced River below Falls Merced River below Falls Merced River below Falls Merced River below Falls Merced River below Falls Merced River below Falls Kern River in ow to Lake Isabella Kern River in ow to Lake Isabella Kern River in ow to Lake Isabella Kern River in ow to Lake Isabella Kern River in ow to Lake Isabella Kern River in ow to Lake Isabella Kern River in ow to Lake Isabella American River below Folsom Lake American River below Folsom Lake American River below Folsom Lake American River below Folsom Lake American River below Folsom Lake American River below Folsom Lake American River below Folsom Lake Kings River below Pine Flat Reservoir Kings River below Pine Flat Reservoir Kings River below Pine Flat Reservoir Kings River below Pine Flat Reservoir Kings River below Pine Flat Reservoir Kings River below Pine Flat Reservoir Kings River below Pine Flat Reservoir Sacramento River above Bend Bridge Sacramento River above Bend Bridge Sacramento River above Bend Bridge Sacramento River above Bend Bridge Sacramento River above Bend Bridge Sacramento River above Bend Bridge Sacramento River above Bend Bridge Sacramento River in ow to Shasta Lake Sacramento River in ow to Shasta Lake Sacramento River in ow to Shasta Lake Sacramento River in ow to Shasta Lake Sacramento River in ow to Shasta Lake Sacramento River in ow to Shasta Lake Sacramento River in ow to Shasta Lake Kaweah River below Terminus Reservoir Kaweah River below Terminus Reservoir Kaweah River below Terminus Reservoir Kaweah River below Terminus Reservoir Kaweah River below Terminus Reservoir Kaweah River below Terminus Reservoir Kaweah River below Terminus Reservoir Stanislaus River below Goodwin Reservoir Stanislaus River below Goodwin Reservoir Stanislaus River below Goodwin Reservoir Stanislaus River below Goodwin Reservoir Stanislaus River below Goodwin Reservoir Stanislaus River below Goodwin Reservoir Stanislaus River below Goodwin Reservoir San Joaquin River in ow to Millerton Lake San Joaquin River in ow to Millerton Lake San Joaquin River in ow to Millerton Lake San Joaquin River in ow to Millerton Lake San Joaquin River in ow to Millerton Lake San Joaquin River in ow to Millerton Lake San Joaquin River in ow to Millerton Lake Tuolumne River below La Grange Reservoir Tuolumne River below La Grange Reservoir Tuolumne River below La Grange Reservoir Tuolumne River below La Grange Reservoir Tuolumne River below La Grange Reservoir Tuolumne River below La Grange Reservoir Tuolumne River below La Grange Reservoir Mokelumne River in ow to Pardee Reservoir Mokelumne River in ow to Pardee Reservoir Mokelumne River in ow to Pardee Reservoir Mokelumne River in ow to Pardee Reservoir Mokelumne River in ow to Pardee Reservoir Mokelumne River in ow to Pardee Reservoir Mokelumne River in ow to Pardee Reservoir

8 California Water Year 2017 Hydrologic Impacts of a Wet 2017 Seasonal (Lead 0.5 Months) Precipitation Heidke Score Many of the hydrologic impacts of DJF Manual Forecasts from 1995 to 2017

California’s prior five-year drought were 49N 47N remedied by the wet conditions. For the 10 45N 10 first time since 2011, runoff in major river 10 43N 10 basins exceeded 150 percent of average, 20 41N in some cases exceeding 200 percent of 39N 37N average. The abundant runoff replenished 20 10 depleted soil moisture. Depleted surface 35N 33N water storage in most of the state’s major 10 31N 10 reservoirs was refilled (excepting Lake 29N Oroville, due to emergency repairs and 27N Average = 7.2 25N reconstruction of its spillways). 125W 121W 117W 113W 109W 105W 101W 97W 93W 89W 85W 81W 77W 73W

-50 -20 -10 10 20 30 40 50 70 100 Total system storage increased only slightly National Weather Service Climate Prediction Center verification of its historical three-month in the interstate Colorado River Basin, December/January/February outlook, as issued two weeks in advance of the forecast. Meteorologists use a metric called the Heidke skill score to evaluate the outlooks. The skill however, remaining at a little over half full. score ranges from -50 to 100, with 100 being a perfect score. A score of zero, represented by The basin, an important water supply source the white areas of the map, means that the outlook had no more skill than simply forecasting long-term average climate conditions. The average skill across the U.S. for the period of 1995 for Southern California, did not experience to 2017, was 7.2, or only slightly better than forecasting average conditions.

2015 2016 2017 Water Year 2011-2017 April-July Runoff at Forecast Points on Major Central Valley Rivers, as Percentage of Average

California Department of Water Resources 9 April-July Unregulated In ow Volume (in millions of acre feet (MAF)) Lake Powell April-July 18 Unregulated Inflow Volume The Colorado River Basin has been 16 experiencing a prolonged period Average: 7.16 MAF (1981-2010) of largely dry conditions, although 14 water year 2017 inflow to Lake Powell ended up slightly above the 12 long-term average.

0 1964 1970 1975 1980 1985 1990 1995 2000 2005 2010 2017 U.S. Bureau of Reclamation

The Colorado River near Moab, Utah, upstream of the confluence with The impacts of land subsidence due to groundwater extraction can be the Green River. Above average precipitation in the Green River Basin seen at this well near Los Banos. When originally constructed the top of during water year 2017 helped Lake Powell inflows exceed the long-term the well casing would have been at the ground surface. Groundwater average. About 85 percent of Colorado River system runoff comes from depletion and land subsidence are examples of lingering drought impacts, 15 percent of the watershed, from the high-elevation mountain areas of and subsidence of the magnitude shown here is not recoverable regardless the Upper Basin above Lake Powell. of how wet subsequent water years are. During the drought years of 2015 and 2016 very high rates of subsidence were observed in parts of the San Joaquin Valley, in the ballpark of a foot per year. A wet 2017 has for the moment put subsidence risks to water infrastructure on hold.

10 California Water Year 2017 the record wetness seen in California, and its large volume of reservoir storage capacity (roughly four times the river’s average annual flow) cannot easily be replenished in a single season. In contrast, a single wet year normally refills the comparatively smaller reservoirs within California, which hold only a fraction of a river’s annual flow.

Groundwater Storage Groundwater storage recovers more slowly than storage in reservoirs, with the specifics of recovery depending on the hydrogeologic Dry private wells in the small unincorporated community of East Porterville were iconic of characteristics of individual groundwater the 2012-2016 drought. DWR worked with partner agencies to build a new distribution system to connect homes with dry wells to a public water system. The first homes were basins. Water levels may recover fairly connected in August 2016, and by end of 2017, more than 750 homes will be connected quickly in shallow basins in direct contact to a reliable water supply. Even though water year 2017 was very wet, there are still many dry and/or contaminated wells in the Central Valley. Throughout 2017, DWR continued to with surface water, while other basins may connect other small communities, such as Hardwick in Tulare County, to public water systems. take many years to recover. Deep confined Groundwater Level Change - Spring 2011 to Spring 2017 aquifers in severely depleted groundwater Increase > 50 feet basins may show no appreciable recovery Increase > 10 to 50 feet Change +/- 10 feet Sacramento River Statewide because they require a very long time to Decrease > 10 to 50 feet (1064 total wells) (3023 total wells) 2.5% recharge. Many of the wells for which DWR Decrease > 50 feet 83.6% 0.0% 0.0% 13.9% receives groundwater level monitoring data North Coast 63.5% 3.6% (174 total wells) North Lahontan 0.5% set records for new lows during the 2012- (102 total wells) 92.0% 2.9% 6.7% 0.0% 89.2% 5.9% 25.7% 16 drought, especially in the San Joaquin 5.2% 0.0% 4.9% Valley and to a lesser extent in the Ventura San Joaquin River (308 total wells) coastal plain. The very wet conditions of 52.9% 4.9% 0.0% 2017 gave many parts of the state access to 41.2% 1.0% Tulare Lake South Lahontan excess surface waters for both planned and (294 total wells) (390 total wells) 15.3% 67.2% 1.5% impromptu groundwater recharge, and fall 42.5% 3.4% 0.0% 3.1% 0.8% San Francisco Bay 35.7% 30.5% 2017 groundwater level data (not available (113 total wells) until the end of the calendar year) should 8.8% 1.8% Colorado River 0.9% (45 total wells) 81.4% 7.1% show the effects of the substantial recharge 4.4% 91.1% 0.0% 0.0% water available. Central Coast 4.4% (60 total wells)

40.0% 16.7% 1.7% 33.3% 8.3%

South Coast (469 total wells) Groundwater Basin 32.0% 3.6% County Boundary 0.4% Hydrologic Region 45.4% 18.6%

California Department of Water Resources 11 SEPTEMBER 2017 California Department of Water Resources 1416 Ninth Street, Sacramento, CA 95814 water.ca.gov/drought